In recent times, the marked development of information technologies (IT) has promoted transition from conventional paper-based two-dimensional maps to two-dimensional electronic maps, and further three-dimensional electronic maps are being constructed to target a wide area such as car navigation systems and GISs (Geographic Information Systems) using computers.
In order to construct a three-dimensional electronic map, it is necessary to obtain height information regarding land features, buildings and other objects, which are components of the three-dimensional electronic map. A laser profiler or LIDAR data have been developed and used as means for easily acquiring such height information. The laser profiler irradiates lasers toward the ground from an airplane and obtains height information based on time differences between the lasers reflected from the ground.
The laser profiler obtains point cloud data constituted of a large number of three-dimensional point data including the height information. In order to construct a three-dimensional electronic map based on the point cloud data, it is necessary to detect land features and three-dimensional shapes of three-dimensional structures such as outer shapes, rooftop shapes, and further roof shapes thereof.
In order to detect the land features and the three-dimensional structure shapes based on the point cloud data, a variety of methods have been conventionally used. In one method, land features and three-dimensional structure shapes such as building shapes are detected and determined through visual observation on a computer display from the height information of the point cloud data. In another method, the land features and the three-dimensional structure shapes are detected and determined by using a satellite image (satellite imagery data) of the ground taken from a satellite together with the height information of the point cloud data, and the satellite image is compared with the height information through visual observation thereof on a computer display. Then, a drawing is made by using a computer to reshape and edit the shapes of three-dimensional structures detected in accordance with the above-mentioned methods.
The conventional methods, however, need a considerable amount of human labor, and the three-dimensional structure shapes are detected and determined depending on skills and experiences of staff members. As a result, the detected and determined three-dimensional structure shapes have quality differences.
Additionally, when the conventional methods are used to construct a three-dimensional map of a city that has a large number of three-dimensional structures in a broad area, considerable human labor and cost are required. For instance, millions of three-dimensional structures are located in 23 wards of Tokyo at present. If one staff member is assumed to be able to deal with 50 structures per a day, it would take more than 200 years to generate all shapes of the three-dimensional structures. Therefore, it is difficult to practically apply the conventional three-dimensional structure shape generation methods to wider areas, for instance, all cities in Japan and all cities around the world.